Wide-band (2.5 - 10.5 µm), high-frame rate IRFPAs based on high-operability MCT on silicon

Abstract

We have previously presented results from our mercury cadmium telluride (MCT, Hg 1-x Cd x Te) growth on silicon substrate technology for different applications, including negative luminescence, long waveband and mid/long dual waveband infrared imaging. In this paper, we review recent developments in QinetiQ's combined molecular beam epitaxy (MBE) and metal-organic vapor phase epitaxy (MOVPE) MCT growth on silicon; including MCT defect density, uniformity and reproducibility. We also present a new small-format (128 x 128) focal plane array (FPA) for high frame-rate applications.A custom high-speed readout integrated circuit (ROIC) was developed with a large pitch and large charge storage aimed at producing a very high performance FPA (NETD ~10mK) operating at frame rates up to 2kHz for the full array. The array design allows random addressing and this allows the maximum frame rate to be increased as the window size is reduced. A broadband (2.5-10.5 µm) MCT heterostructure was designed and grown by the MBE/MOVPE technique onto silicon substrates. FPAs were fabricated using our standard techniques; wet-etched mesa diodes passivated with epitaxial CdTe and flip-chip bonded to the ROIC.The resulting focal plane arrays were characterized at the maximum frame rate and shown to have the high operabilities and low NETD values characteristic of our LWIR MCT on silicon technology.

Nondestructive Monitoring of Defect Evolution in Epitaxial CdTe Thin Layers Grown on Si(111)

“…Cadmium telluride (CdTe) plays a significant role as one of the most important materials for infrared and gamma detectors and for solar cells in the form of bulk crystals, thin/thick layers, and quantum dots. − Heteroepitaxial growth of CdTe on Si substrate is a key technology for low cost mercury cadmium telluride (MCT) infrared detectors . The main interest in using CdTe/Si as substrate for the epitaxial growth of MCT is the trend toward mega-pixel focal-plane arrays and the possibility of integrating them with Si-based readout electronics . CdTe/Si heterojunctions are also a promising way to achieve large-area, thick and high-quality crystals for X-ray and gamma ray detectors for medical imaging applications working up to 140 keV energy range since bulk CdTe crystals are expensive, extremely soft, and tend to develop a high density of dislocations .…”

“…5 The main interest in using CdTe/Si as substrate for the epitaxial growth of MCT is the trend toward mega-pixel focal-plane arrays and the possibility of integrating them with Si-based readout electronics. 6 CdTe/Si heterojunctions are also a promising way to achieve large-area, thick and high-quality crystals for X-ray and gamma ray detectors for medical imaging applications working up to 140 keV energy range 7 since bulk CdTe crystals are expensive, extremely soft, and tend to develop a high density of dislocations. 8 Although remarkable progress has been achieved using nominal and misoriented Si(100), Si(111), and Si(211) substrates, the large difference in thermal expansion coefficients and the lattice constant mismatch of approximately 19% usually result in a high density of dislocations and other stacking defects, especially close to the interface.…”